Researchers in the surgical arts have been working for many years to develop new techniques and materials for use as grafts to replace or repair damaged or diseased tissue structures, particularly bones and connective tissues, such as ligaments and tendons, and to hasten fracture healing. It is very common today, for instance, for an orthopedic surgeon to harvest a patellar tendon of autogenous or allogenous origin for use as a replacement for a torn cruciate ligament. The surgical methods for such techniques are well known. Further, it has become common for surgeons to use implantable prostheses formed from plastic, metal and/or ceramic materials for reconstruction or replacement of physiological structures. Yet, despite their wide use, presently available surgically implanted prostheses present many attendant risks to the patient. Therefore, surgeons are in need of a non-immunogenic, high tensile strength graft material which can be used for the surgical repair of bone, tendons, ligaments and other functional tissue structures.
More recently researchers have been working to develop biological tissues for use as implants and for use in the repair of damaged or diseased tissues, since plastic and polymer materials have drawbacks in these medical applications. While plastics and polymers may have some desirable mechanical properties (e.g., tensile strength), plastics have been found to become infected and in vascular applications plastics have been reported as inducing thrombogenesis.
Tubular prostheses made from natural tissues have been widely used in recent years in the surgical repair and replacement of diseased or damaged blood vessels in human patients. Natural tissue prostheses fall into three general classes: Autogenous, homologous, and heterologous prostheses. Autogenous material tissue prostheses are prepared from tissues taken from the patient's own body (e.g., saphenous vein grafts). Use of such prostheses eliminates the possibility of rejection of the implanted prosthesis, but requires a more extensive and time-consuming surgical intervention with attendant risks to the patient. Homologous natural tissue prostheses are prepared from tissue taken from another human, while heterologous natural tissue prostheses are prepared from tissue taken from a different species. The use of homologous and heterologous umbilical cord vessels as, e.g., vascular and ureteral prostheses are disclosed in U.S. Pat. Nos. 3,894,530; 3,974,526; and 3,988,782.
In addition, autogenous vascular prostheses prepared from sheets of pericardial tissue have been disclosed by Yoshio Sako, "Prevention of Dilation in Autogenous Venous and Pericardial Grafts in the Thoracic Aorta," Surgery, 30, pp. 148-160 (1951) and by Robert G. Allen and Francis H. Cole, Jr., "Modified Blalock Shunts Utilizing Pericardial Tube Grafts," Jour. Pediatr. Surg., 12(3), pp. 287-294 (1977). Heterologous vascular prostheses prepared from sheets of porcine pericardial tissue have been disclosed by Ornvold K. et al., "Structural Changes of Stabilized Porcine Pericardium after Experimental and Clinical Implantation," in Proc. Eur. Soc. for Artif Organs, Vol. VI, Geneva, Switzerland (1979).
The necessary characteristics of a tubular vascular prosthesis are biological compatibility, adequate strength, resistance to infection, resistance to biological degradation, non-thrombogenicity and lack of aneurysm formation. As used in this application, the term biological compatibility means that the prosthesis is non-toxic in the in vivo environment of its intended use, and is not rejected by the patient's physiological system (i.e., is non-antigenic). Furthermore, it is desirable that the prosthesis be capable of production at an economical cost in a wide variety of lengths, diameters and shapes (e.g., straight, curved, bifurcated), be readily anastomosed to the patient's body and to other tubular prostheses of the same or different type, and exhibit dimensional stability in use.
As disclosed in U.S. Pat. No. 4,902,508, vascular grafts constructs comprising intestinal submucosal tissue have been previously described and utilized to replace damaged or diseased vascular tissues. The vascular graft constructs were prepared by inserting a glass rod of the appropriate diameter into the lumen of the submucosal tissue and hand-suturing along the seam of the submucosal tissue. The submucosal tissue vascular grafts are aseptically fabricated during surgery and typically take a surgeon about one half hour to prepare. Therefore to avoid spending time preparing the graft constructs during surgery, premade, presterilized grafts of different diameters are desirable.
Preparation of a tubular prosthesis of the correct length and shape increases the ease of implantation and enhances the functionality of the implant. For example, a tubular prosthesis that is too long for the intended application may kink after implantation, whereas implantation of a prosthesis that is too short places excessive tension on the anastomoses at its ends, thereby resulting in trauma to said anastomoses. Thus, it would be highly desirable to provide an array of tubular prosthesis that vary in diameter and that can be cut transversely to a desired length at any point between its ends without otherwise substantially damaging the prosthesis.
The present invention is directed to a tubular prosthesis comprising submucosal tissue and methods for preparing such a prosthesis. Submucosal tissue, prepared in accordance with the present invention, has been previously described as a biocompatible, non-thrombogenic graft material that enhances the repair of damaged or diseased host tissues. Numerous studies have shown that warm-blooded vertebrate submucosa is capable of inducing host tissue proliferation, remodeling and regeneration of tissue structures following implantation in a number of in vivo microenvironments including lower urinary tract, body wall, tendon, ligament, bone, cardiovascular tissues and the central nervous system. Upon implantation, cellular infiltration and a rapid neovascularization are observed and the submucosa material is remodeled into host replacement tissue with site-specific structural and functional properties.
Submucosal tissue can be obtained from various tissue sources, harvested from animals raised for meat production, including, for example, pigs, cattle and sheep or other warm-blooded vertebrates. More particularly, the submucosa is isolated from a variety of tissue sources including the alimentary, respiratory, intestinal, urinary or genital tracts of warm-blooded vertebrates. In general, submucosa is prepared from these tissue sources by delaminating the submucosal from both the smooth muscle layers and the mucosal layers. The preparation of intestinal submucosa is described and claimed in U.S. Pat. No. 4,902,508, the disclosure of which is expressly incorporated herein by reference. Urinary bladder submucosa and its preparation is described in U.S. Pat. No. 5,554,389, the disclosure of which is expressly incorporated herein by reference. Stomach submucosa has also been obtained and characterized using similar tissue processing techniques. Such is described in U.S. patent application Ser. No. 60/032,683 titled STOMACH SUBMUCOSA DERIVED TISSUE GRAFT, filed on Dec. 10, 1996. Briefly, stomach submucosa is prepared from a segment of stomach in a procedure similar to the preparation of intestinal submucosa. A segment of stomach tissue is first subjected to abrasion using a longitudinal wiping motion to remove the outer layers (particularly the smooth muscle layers) and the luminal portions of the tunica mucosa layers. The resulting submucosa tissue has a thickness of about 100 to about 200 micrometers, and consists primarily (greater than 98%) of acellular, eosinophilic staining (H&E stain) extracellular matrix material.